/**
给定一个二叉树，检查它是否是镜像对称的。


例如，二叉树 [1,2,2,3,4,4,3] 是对称的。

    1
   / \
  2   2
 / \ / \
3  4 4  3

*/


/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isSymmetric(TreeNode root) {
      return  bfs(root.left,root.right);
    }
    public boolean bfs(TreeNode p,TreeNode q){
        //boolean temp=true;
        if(p==null && q==null){
            return true;
        }
        if(p==null || q==null){
            return false;
        }
        if(p.val!=q.val){
            return false;
        }
   
        return bfs(p.left,q.right) && bfs(p.right,q.left);
    }
}